As a vehicle drive device, a device has been proposed in which the left and right axles of a vehicle are connected to a differential apparatus and drive power is transmitted to the differential apparatus via a speed reduction mechanism using an electric motor coaxially disposed on the outer circumferential side of one of the axles (see e.g., Patent document 1).
This drive device 100 is, as shown in FIG. 16, equipped with an electric motor 102 for driving axles, a planetary gear reducer 112 for reducing the drive rotation speed of this electric motor 102, and a differential apparatus 113 for distributing the output of this planetary gear reducer 112 to the left and right axles 110A and 110B of a vehicle, wherein the planetary gear reducer 112 and the electric motor 102 are disposed coaxially with each other on the outer circumferential side of the axle 110B connected to the differential apparatus 113. Furthermore, the sun gear 121 and the planetary carrier 123 of the planetary gear reducer 112 are connected to the rotor 115 of the electric motor 102 and the differential case 131 of the differential apparatus 113, respectively, the ring gear 124 of the planetary gear reducer 112 is rotatably accommodated in the reducer case 111 that is secured to a vehicle body, and a hydraulic brake 128 for applying a braking force to the ring gear 124 by engaging the ring gear 124 with the reducer case 111 is provided between the ring gear 124 and the reducer case 111.
When the braking force is applied to the ring gear 124 by the hydraulic brake 128, the ring gear 124 is secured to the reducer case 111, and the drive power input from the rotor 115 of the electric motor 102 to the sun gear 121 is transmitted to the differential case 131 of the differential apparatus 113 while speed is reduced by a preset reduction ratio. The drive power transmitted to the differential case 131 is distributed to the left and right axles 110A and 110B of the vehicle by the differential apparatus 113. Moreover, when the braking force applied from the hydraulic brake 128 is shut off, the ring gear 124 rotates freely with respect to the reducer case 111. Hence, for example, when the braking force applied by the hydraulic brake 128 is shut off in a state in which the rotation speed of the axles 110A and 110B is higher than that required for the driving of the electric motor 102, the ring gear 124 idly rotates inside the reducer case 111 depending on extra rotation on the sides of the axles 110A and 110B, and the rotations of the axles 110A and 110B are not input to the electric motor 102. Hence, in the case that the driving and regeneration of the electric motor 102 are not necessary, accompanied rotation of the electric motor 102 can be prevented by shutting off the application of the braking force of the hydraulic brake 128, thereby attaining improvement in fuel consumption.